Inkjet recording is a recording system for forming characters or images, comprising directly jetting ink droplets from a very fine nozzle to a recording medium, and depositing the ink droplets on the recording medium. This system has some advantages such that not only the usable device shows excellent operability at a low level of noise, but also the coloration is facilitated and a plain sheet of paper can be used as a recording medium. Therefore, in recent years, this system has been widely used in inkjet printers.
As the colorants for use in inkjet printers, from the viewpoints of color development and jetting reliability, water-soluble dyes have been mainly used. However, the water-soluble dyes are poor in water resistance, so that feathering occurs in the printouts.
Therefore, for the purpose of improving the water resistance and character quality, as an ink containing an aqueous dispersion of polymer particles containing a hydrophobic dye, (i) an ink containing an oil-in-water emulsion made of a solution of a hydrophobic dye and vinyl polymer particles as disclosed in Japanese Patent Laid-Open No. 54-58504, (ii) an ink containing water-insoluble vinyl polymer latex particles which are impregnated with a disperse dye by heating as disclosed in Japanese Patent Laid-Open No. 55-139471, and (iii) an ink containing polymer latex particles containing a hydrophobic dye as disclosed in Japanese Patent Laid-Open No. 58-2366.
However, in the above inks (i) and (ii), when printing is performed for a long period of time using an ink containing polymer particles having as a major component a linear alkyl (meth)acrylate and an aromatic (meth)acrylate, a film derived from the polymer particles is formed on the head and the ink outlet of a printer, which may cause blurriness or distortion in the printout, and thus printing reliability may be impaired.
Also, in the above ink (iii), there is a defect that the optical density and character quality, in particular, sharpness of printed characters and images, are not sufficient.
Further, in the above inks (i), (ii) and (iii), there are defects that the storage stability of the aqueous dispersion of polymer particles is not sufficient; that the solvent resistance of the aqueous dispersion to a solvent formulated in the ink is not sufficient; that the particle diameter of the aqueous dispersion is large; and that the viscosity of the ink is high.